It has now become extremely common for the modern office worker to use video display terminals. The use of such terminals in some job assignments goes on for hours on end--often without rest of the eyes or relief of the worker. Worker fatigue, especially through strain of the eyes, has become common.
Unlike the former clerical tasks accomplished on paper, video display terminals have special viewing problems. A summary of these viewing problems can be instructive.
First, the video display terminal is a light source. Many portions of the screen emit light, especially when color terminals are used. Second, the patient is required to focus on and observe closely the light emitting screen at an information area. Such an information area is usually the light emitting "cursor" on the surface terminal where information of computer input or output is displayed. Third, and due the fact that the video display terminals are all covered with a transparent glass coating, the terminals themselves are sources of reflection, these reflections interfering with the subject matter to be viewed. Artificial and natural light is reflected from the screens into the eyes of the concentrating viewer. In short, viewing conditions that would never be tolerated in an ordinary reading situation are required viewing conditions when working with video display terminals.
The eye strain problem associated with video display terminals is now notorious. Ordinances and laws are being passed for the safety of the video display terminal worker.
Obvious corrective measures have been undertaken. These measures include glasses with ultra violet filters, infrared filters, and anti reflective coatings. Similarly, polarizing filters have been placed on the surfaces of the video display terminal screens. All this has been coupled with improved abient lighting systems (usually with downward collimated illuminating light).
Unfortunately, the difficulties of the video display worker are usually compounded with age. It is well known that the eye undergoes an aging process which makes accommodation for the viewing of objects at "reading distance" increasingly more difficult. At least two effects contribute to this aging effect, which effect requires most adults over 45 years of age to require "reading glasses." The lens of the eye becomes less elastic with age. The eye muscles that normally produce accommodation, must work harder to achieve accommodation.
The traditional cure of the emmetrope (person with normal vision) loosing his power of accommodation is to supply so-called "reading glasses." Reading glasses are nothing more than a positive spherical prescription.